Interpretive Summary: Limited progress in understanding parasite proteins hinders our rapid development of novel vaccines against coccidia. Coccidiosis is the most important protozoan disease of poultry due to its significant economic impact on poultry industry. At least, seven species of Eimeria have been recognized which infect chickens and they parasitize specific areas within the digestive tract with different degrees of pathogenicity and immunogenicity. In this research paper, ARS scientists in collaboration with scientists at University of Osaka and University of Hiroshma developed new sets of chicken monoclonal antibodies (mAbs) that detect proteins of Eimeria spp. One of these mAbs, 6D-12-G10, was found to recognize a conoid antigen of EA sporozoites and significantly inhibited the sporozoite invasions of host T lymphocytes in vitro. Furthermore, some of these chicken mAbs also bound the tachyzoites of Neospora caninum and Toxoplasma gondii. In this study scientists also discovered that these antibodies detect antigens on Cryptosporidium spp which is an important pathogen of human and mammals. These results enhance our understanding of the nature of coccidia antigens which can be used in vaccine. The results of this paper will help poultry industry to design better vaccines for coccidiosis.

Technical Abstract:
In a previous study, we have developed several chicken monoclonal antibodies (mAbs) against Eimeria acervulina (EA) in order to identify potential ligand molecules of Eimeria. One of these mAbs, 6D-12-G10, was found to recognize a conoid antigen of EA sporozoites and significantly inhibited the sporozoite invasions of host T lymphocytes in vitro. Furthermore, some of these chicken mAbs showed cross-reactivities with several different avian Eimeria spp. and the mAb 6D-12-G10 also demonstrated cross-reactivities with the tachyzoites of Neospora caninum and Toxoplasma gondii. Cryptosporidium spp. are coccidian parasites closely rlated to Eimeria spp., and especially C. parvum is important cause of diarrhea in human and mammals. In the present study, to assess that the epitopes recognized by these chicken mAbs could exist on Cryptosporidium parasites, we examined the cross-reactivity of these mAbs with Cryptosporidium spp. using an indirect immunofluorescent asssay (IFA) and western blotting analyses. In IFA by chicken mAbs, the mAb 6D-12-G10 only showed a immunofluorescence staining at the apical end of sporozoites of C. parvum and C. muris, and merozoites of C. parvum. Western blotting analyses revealed that the mAb 6D-12-G10 reacted with the 48 kDa molecular weight band of C. parvum and C. muris oocysts antigens, 5D-11 reacted the 155-kDa of C. muris. Furthermore, these epitopes appeared to be periodate insensitive. These results indicate that the target antigen recognized by these chicken mAbs might have a shared epitope which is present on the apical complex of apicomplexan parsites.